The application of otoplastics for attaching hearing aids to the auditory canal generally requires a ventilation bore to avoid inflammations of the auditory canal skin resulting from the moisture buildup for example, and to avoid injuries to the eardrum due to excess or negative pressure for example. The ventilation bore can have a relatively large diameter, particularly for certain high-tone hearing losses, thereby ensuring that as much low tone sound as possible reaches the ear drum in a natural manner. The more open the auditory canal is, the better the otoplastic is accepted. A so-called tube holder is used in borderline cases, which only minimally reduces the lumen (opening) of the auditory canal. Open otoplastics of this type are nevertheless disadvantageous in that the amplified sound can come back out of the ear, thus leading to unpleasant feedback. The actual amplification of the hearing aid which can be used is thereby restricted.
Specific circuits for the frequency-specific restriction of amplification at the feedback frequency have thus been used in hearing aids in order to avoid these types of feedback. Alternatively or in addition, an active feedback compensator is integrated into the hearing aid, said feedback compensator eliminating the feedback frequencies in the frequency response. 10 db amplification reserves can be achieved in this manner.
Furthermore, an IdO hearing aid with a vent and/or ventilation bore is known from the publication WO 92/21218. A Helmoholtz resonator is attached to the vent in order to attenuate the frequency. The attenuated frequency is determined, among other things, by the length of the vent and the volume in the housing.
A hearing aid with a stepped body is disclosed in the publication DE 199 43 809 A1, said stepped body protruding into the user's outer auditory canal. The stepped body reduces the free volume between the otoplastic and the ear drum and also enables additional acoustic measures for influencing the frequency response. One or more resonators, Helmholtz resonators for example, can be arranged in the stepped body, said resonators being attached to the sound channel of the stepped body and effecting an amplified attenuation of selected frequency ranges.